Sumner Redstone, the media mogul, is 91 and worth $6.2 billion. While he's engaged in plenty of philanthropy, he hasn't signed the Giving Pledge and has yet to make much of a dent in giving away his large fortune. Nor is there much time left to do that.

Which is why it's good to know more about his daughter, Shari Redstone. Shari has long been Sumner's heir apparent in business matters.She's been a top executive in his media empire for years, but she's also the logical person to play a leadership role in building the Redstone philanthropic legacy, despite the legendary conflicts she has had with her father over the years and the fact that much of his wealth will go to a trust for his grandchildren.

Why? Because she cares a lot about philanthropy and has experience in the social sector.

Before saying more about Shari, here are a few things to know about where things stand with Sumner's philanthropy:

Redstone has long been involved in philanthropy, but not in a super elaborate fashion. Unlike many older billionaires, he didn't gradually shift his attention from making money to giving it away. Instead, Redstone has stayed deeply involved in business matters even as he hit his tenth decade of life. One reason that business titans may avoid large-scale giving is that they don't want to reduce control of their empires by selling large amounts of stock to enable big giving. So it's significant that the Wall Street Journal recently reported that Redstone has sold hundreds of millions of dollars of Viacom and CBS stock in recent weeks. That could indicate a coming turn to large-scale philanthropy as Redstone hits his final years.

While Redstone does have a foundation, its relatively modest assets stand at just $6.9 million as of the end of 2012. It has mainly been a pay-as-you-give type of operation. So in 2012, Redstone donated $32 million to his foundation, and in turn it gave away $29 million in grants. The foundation hasn't had much in the way of staff and spent just $1,000 on administrative overhead in 2012. Its website states that Redstone has given away $216 million to charitable causes. Those causes are something of a grab bag, and include: medical research, global poverty, the arts, underprivileged kids in Los Angeles, and a number of higher ed institutions.

Redstone has made a few big gifts in recent years, such as the $24 million he pledged to cancer research at the University of Southern California, $18 million to build a law school building at Boston University, and $10 million to support public interest fellowships at Harvard Law School. Back in 2007, he made a $105 million commitment for medical research to several healthcare institutions.

These are decent-size gifts, but nothing compared to what the Redstone fortune could underwrite. And notably, Redstone has never really committed himself to one signature cause.

All of which is to say that the heavy lifting of giving away billions of dollars of Redstone wealth hasn't really begun and is likely to be done mainly by his heirs. Exactly how this will play out is hard to say, since Redstone's grandchildren will be the beneficiaries of a family trust that will control most of his wealth. Moreover, Redstone has said that this trust will be precluded from selling the family's controlling stake in his business empire, which would limit how much cash is available for philanthropy.

Still, it would stand to reason that some of this fortune will find its way to philanthropy and Shari will play a role here.

Now, about Shari Redstone: After graduating from BU's law school, she started her career as a criminal defense lawyer, then switched to corporate law but found it too dull, and then focused on being a full-time mom to three children. She was considering studying social work when her father convinced her to come and work for him.

Clearly, though, the interest in social issues never went away. She's sat on a number of nonprofit boards over recent years, including that of Combined Jewish Philanthropies (she's off that one), the Dana-Farber Cancer Institute (still on that one), the John F. Kennedy Library (still on that one), and, more recently, Our Time, a group that stands up for young Americans.

Shari used to also sit on the board of the National Center on Addiction and Substance Abuse (CASA). One of the projects she was involved in there was launching a dinner program that encouraged family members to spend more time together to prevent teenagers from using drugs.

One last thing about Sheri Redstone: She owns 20 percent of her father's media empire, and is thus a billionaire in her own right, although she's not listed as such by Forbes. So whatever else happens, this a woman with some serious money at her disposal.

Oh, and those grandchildren who will get the bulk of Sumner Redstone's wealth? Three of them are Shari's kids.